LED drive circuit for SCR dimming

1. A LED drive circuit for SCR dimming comprising: an external controller configured to convert AC voltage from a power network to AC voltage with a lacked phase by phase controlling the voltage through a thyristor; and a LED driver comprising: a bridge rectifier configured to shape the AC voltage with the lacked phase output into a unidirectional pulse DC voltage, and deliver the pulse DC voltage to a main circuit; a current controlling circuit which comprises a current detecting signal outputted from the main circuit and a controlling signal output from the phase angle detecting circuit, and wherein the current controlling circuit outputs a current reference signal to the main circuit to control and adjust the current; a main circuit configured to receive the pulse DC voltage signal output from bridge rectifier and a current reference signal output from a current detecting circuit, and after being modulated by a pulse width modulation circuit further configured to convert its voltage and output DC voltage to a LED load and a current detecting signal to a current controlling circuit; and a phase angle detecting circuit configured to shape the AC voltage signal output with the lacked phase from the external controller into a saw-tooth wave pulse signal, whose peak value changes according to a variation of thyristor trigger phase angle wherein the saw-tooth voltage signal is converted to a level signal, which changes in proportion to a peak variation of the saw-tooth wave pulse signal, and then outputs the level signal to the current controlling circuit as the output controlling signal from the phase angle detecting circuit.

2. The LED drive circuit according to claim 1 , wherein the main circuit can control the constant current and adjust the output current to regulate the output current and adjust the illumination intensity of the LED, and wherein the phase angle detecting circuit and the current controlling circuit are isolated circuits.

3. The LED drive circuit according to claim 2 , wherein the phase angle detecting circuit comprises a first resistor, a second resistor, a third resistor, a first capacitor, a second capacitor, a first diode, a second diode, a third diode, a transistor, and an optocopuler.

4. The LED drive circuit according to claim 3 , wherein the anodes of a first diode and second diode are connected to output ends of the external controller, cathodes of the first diode and the second diode and one end of the first resistor are connected, a second end of the first resistor is connected to a base of the first transistor while an emitter end of the first transistor is connected to a power ground, the cathode of the light emitting diode in the optocoupler is connected to a collector end of a first transistor, an anode of the optocoupler is connected to one end of the third resistor, the other end of third resistor is connected to a reference power supply, a collector of a photistor in the optocoupler is connected to an anode of the third diode, a first end of the second resistor and a first end of the first capacitor, a second end of second resistor is connected to the reference power supply, an emitter of the photistor in the optocopuler is connected to a signal ground, a cathode of the third diode is connected to a first end of second capacitor, while the second end of second capacitor is connected to the second end of first capacitor, and the signal ground.

5. The LED drive circuit according to claim 4 , wherein the phase angle detecting circuit is configured to detect and shape a signal on the phase angle signal.

6. The LED drive circuit according to claim 5 , wherein the current controlling circuit further comprises a third resistor, a fourth resistor, a fifth resistor, a sixth resistor, a seventh resistor, a third capacitor, a fourth capacitor, a first transistor, and an integrated operational amplifier.

7. The LED drive circuit according to claim 6 , wherein a base of the first transistor is connected to a cathode of the third diode and one end of the second capacitor, a collector of the transistor is connected to an end of the reference power supply, an emitter of transistor is connected to one end each of the third resistor and the fourth resistor, a second end of the third resistor is connected to the signal ground, a second end of the fourth resistor is connected to a negative input terminal of the integrated operational amplifier and to one end each of the fifth resistor, sixth resistor and the third capacitor, a second end of the fifth resistor is connected to a first end of seventh resistor, a second end of the seventh resistor is connected to the signal ground, a positive input terminal of the integrated operational amplifier is connected to an end of a second reference power supply, a second end of the sixth resistor is connected to one end of the fourth capacitor, and a second end of fourth capacitor is connected to a second end of the third capacitor and an output terminal of integrated operational amplifier.

8. The LED drive circuit according to claim 7 , wherein a signal from the output terminal of integrated operational amplifier is a current reference signal, and the output current of LED driver is controlled by the main circuit.

9. The LED drive circuit according to claim 1 , wherein the phase angle detecting circuit consists of a first resistor, a second resistor, a first capacitor, a second capacitor, a third diode, first transistor, a first optocoupler and a second optocoupler.

10. The LED drive circuit according to claim 9 , wherein a branch is formed comprising consists an LED in the first optocoupler and an LED in the second optocouler having an anti-parallel connection, and the first resistor in series; a first and second ends of the branch connected to the respective output ends of the external controller; collectors of the each photistor are connected together, and then connected to an anode of the third diode, an end of the second resistor and an end of the first capacitor; a second end of the second resistor is connected to an end of the second reference power supply; emitters of the photistors connected to the signal ground; a cathode of the third diode connected to one end of the second capacitor while a second is connected to a second end of the first capacitor and to the signal ground.

11. The LED drive circuit according to claim 10 , wherein the current controlling circuit comprises the third resistor, the fourth resistor, the fifth resistor, the sixth resistor, the seventh resistor, the third capacitor, the fourth capacitor, the first transistor, and the integrated operational amplifier.

12. The LED drive circuit according to claim 11 , wherein the base of first transistor is connected to the cathode of the third diode and one end of the second capacitor, the collector of integrated operational amplifier is connected to an end of the first reference power supply, and the emitter of the transistor is connected to one end each of the third resistor and the fourth resistor; the second end of the third resistor is connected to the signal ground; a second end of the fourth resistor is connected to the negative input terminal of the integrated operational amplifier, one end each of the fifth resistor, sixth resistor and the third capacitor; a second end of the fifth resistor is connected to one end of the seventh resistor, and a second end of the seventh resistor is connected to the signal ground; a positive input terminal of the integrated operational amplifier is connected to an end of a second reference power supply; and a second end of the sixth resistor is connected to one end of the fourth capacitor while a second end of the fourth capacitor is connected to a second end of the third capacitor and to an output terminal of the integrated operational amplifier.

13. The LED drive circuit for SCR dimming as claimed in claim 1 , wherein the phase angle detecting circuit comprises a first resistor, second resistor, first capacitor, second capacitor, first diode, second diode, third diode, and an optocoupler.

14. The LED drive circuit according to claim 13 , wherein anodes of the first diode and the second diode are connected individually to a respective separate one of output ends of the external controller; cathodes of the first diode and the second diode and a first end of the first resistor are connected; a second end of the first resistor is connected to an anode of a LED in the optocoupler; a cathode of the LED in optocoupler is connected to the power ground; a collector of the photistor in the optocoupler is connected to an anode of the third diode one end each of the second resistor and the first capacitor; a second end of second resistor is connected to an end of the first reference power supply; an emitter of the photistor in the optocoupler is connected to the signal ground; and a cathode of the third diode is connected to one end of the second capacitor while the other end of second capacitor is connected to a second end of the first capacitor and the signal ground.

15. The LED drive circuit according to claim 14 , wherein the current controlling circuit consists of a third resistor, a fourth resistor, a fifth resistor, a sixth resistor, a seventh resistor, a third capacitor, fourth capacitor, a transistor, and an integrated operational amplifier, wherein a base of the transistor is connected to a cathode of third diode and a first end of the second capacitor, a collector of the transistor is connected to an end of the first reference power supply, and an emitter of transistor is connected to a first end of the third resistor and a first end of the fourth resistor; a second end of the third resistor is connected to the signal ground, while a second end of the fourth resistor is connected to a negative input terminal of the integrated operational amplifier, a first end of the fifth resistor, a first end of a sixth resistor, and a first end of the third capacitor; a second end of the fifth resistor is connected to a first end of the seventh resistor, and a second end of the seventh resistor is connected to the signal ground; a positive input terminal of the integrated operational amplifier is connected to one end of the second reference power supply; a second end of the sixth resistor is connected to a first end of the fourth capacitor, while a second end of the fourth capacitor is connected to a second end of the third capacitor and an output terminal of the integrated operational amplifier; wherein the signal in the output terminal of integrated operational amplifier is the current reference signal, and the output current of the LED driver is controlled by the main circuit.

16. The LED drive circuit for SCR dimming as claimed in claim 1 , wherein the phase angle detecting circuit and the current controlling circuit are non-isolated circuits and the main circuit is a non-isolated circuit with constant current output, wherein the phase angle detecting circuit further comprises a first resistor, a second resistor, a first capacitor, a second capacitor, a first diode, a second diode, a third diode, and a second transistor, and further wherein anodes of the first diode and the second diode are connected to two output ends of the external controller respectively; cathodes of the first diode and the second diode, and a first end of the first resistor are connected; a second end of the first resistor is connected to a base of the second transistor while a emitter end of the second transistor is connected to ground; a collector of the second transistor is connected to an anode of the third diode, one end each of the second resistor and the first capacitor; a second end of the second resistor is connected to an end of the first reference power supply; and a cathode of the third diode is connected to one end of the second capacitor while the other end of second capacitor is connected to the other end of first capacitor and to ground.

17. The LED drive circuit for SCR dimming as claimed in claim 16 , wherein the current controlling circuit consists of a third resistor, a fourth resistor, a fifth resistor, a sixth resistor, a seventh resistor, a third capacitor, a fourth capacitor, a transistor, and an integrated operational amplifier, wherein a base of the transistor is connected to a cathode of the third diode and one end of the second capacitor, a collector of transistor is connected to one end of the first reference power supply, and an emitter of transistor is connected to one end of third resistor and the fourth resistor; a second end of the third resistor is connected to ground, while a second end of the fourth resistor is connected to a negative input terminal of the integrated operational amplifier, one end of the first resistor, one end of the sixth resistor, and one end of the third capacitor; A second end of the fifth is connected to one end of the seventh resistor, and a second end of the seventh resistor is connected to ground; a positive input terminal of the integrated operational amplifier is connected to one end of the second reference power supply; a second end of the sixth resistor is connected to one end of the fourth capacitor while a second end of fourth capacitor is connected to a second end of the third capacitor and an output terminal of the integrated operational amplifier; and wherein a signal in the output terminal of integrated operational amplifier is a current reference signal, and an output current of the LED driver is controlled by the main circuit.

18. The LED drive circuit for SCR dimming as claimed in claim 17 , wherein the phase angle detecting circuit consists of first resistor, a second resistor, an eighth resistor, a ninth resistor, a tenth resistor, a first capacitor, a second capacitor, a third diode, a second transistor, and a third transistor wherein ends of the first resistor and the ninth resistor are connected to respective different two output ends of the external controller; a second end of the first resistor is connected to a base of the third transistor and one end of the eight resistor while a second end of the ninth resistor is connected to a base of the second resistor and a first end of the tenth resistor; a second end of the eighth resistor and the tenth resistor and emitters of the third transistor and the second transistor are connected to the ground; collectors of second transistor and the third transistor are connected to an anode of the third diode, one end each of the second resistor and the first capacitor; and a second end of second resistor is connected to one end of the first reference power supply; and a cathode of the third diode is connected to one end of the second capacitor while a second end of the second capacitor is connected to a second end of the first capacitor and to ground.

19. The LED drive circuit for SCR dimming as claimed in claim 18 , wherein the current controlling circuit comprises of a third resistor, a fourth resistor, a fifth resistor, a sixth resistor, a seventh resistor, a third capacitor, a fourth capacitor, a first transistor, and an integrated operational amplifier wherein a base of first transistor is connected to a cathode of the third diode and one end of the third capacitor, a collector of first transistor is connected to one end of the first reference power supply, and an emitter of the transistor is connected to one end each of third resistor and the fourth resistor; a second end of third resistor is connected to ground while a second end of the fourth resistor is connected to a negative input terminal of the integrated operational amplifier, one each of the fifth resistor, sixth resistor, and the third capacitor; a second end of the fifth resistor is connected to one end of the seventh resistor and a second other end of the seventh resistor is connected to ground; a positive input terminal of the integrated operational amplifier is connected to one end of the second reference power supply; a second end of the sixth resistor is connected to one end of the fourth capacitor while a second end of the fourth capacitor is connected to a second end of the third capacitor and an output terminal of the integrated operational amplifier; and wherein a signal in an output terminal of the integrated operational amplifier is the current reference signal, and an output current of LED driver is controlled by main circuit.